Distillate fuel manufacture involving extraction with liquid hf



N. FRAGEN DISTILLTE FUEL MANUFACEURE INVOLVING oct. 17; w50

EXTRACTION WITH LIQUID HF Filed DBC. l3,` 1947 atented ct. `17, 195'() DISTILLATE FUEL MANUFACTURE INVOLV- ING EXTRACTION WITH LIQUID HF Nathan Fragen, Hammond, Ind., assignor to Standard Oil Company, Chicago, Ill., a corporation of Indiana Application December 13, 1947, Serial No. 791,511

This invention relates to distillate fuel manufacture and it pertains more specifically to the manufacture of high quality distillate fuels, such as heater oil, furnace oil and Diesel fuel from high sulfur crudes such, for example, as West Texas crude oil. i

Heretofore distillate fuels have been produced as Icy-products in the manufacture of gasoline and such fuels of relatively high quality could be obtained from fractions of the virgin crude oil or from the cracking of virgin crude oil or from mixtures of virgin and cracked products. The phenomenal increase in demand for distillate fuels brought about by increased use of oil burners, replacement of steam locomotives by Diesel engines on railways, etc., coupled with the fact that high quality crude oils, such as Mid-Continent crude, are insumcient to meet demands and hence must be replaced by high sulfur crude oils has presented a serious problem to the oil refining industry. An object of this invention is to provide an improved method and means for obtaining the necessary amounts of high quality distillate without sacrificing yields or quality of gasoline andA other products produced when high sulfur crude oil is employed as a charging stock. An important characteristic of an acceptable distillate fuel is that it have a low sulfur content. Generally speaking, the sulfur content should not exceed about .5% and even a lower sulfur limitV is desirable (although for some purposes a sulfur content as high as 1% maybe tolerated). Distillate fuel fractions from Mid- Continent virgin gas oil contain only about .1 to .2% sulfur and even the cycle stock from the cracking of such gas oil has a sulfur content not substantially higher than about .2%. West Texas gas oil, however, is characterized by a sulfur content of the order of about 2% and the cycle stock from the cracking of such gas oil has sulfur `contents upwards of 1%, e. g. approximately 1.5%

or more. An object of the invention is to provide distillate fuels from high sulfur crudes without interfering with maximum gasolineproduction, said distillate fuels having a sulfur content not substantially higher than about .5 %.A ,Il

Another desired characteristic of a distillate 7 Claims. (o1. 19a- 13)A fuel is its freedom from tendencies toward `coke `Which will be hereinafter defined or characterized by setting forth the precise test for its determination. The BQI of a distillate fuel is an index of its quality for its intended use which is Comparable `to octane number as a quality index for gasoline. For satisfactory burning qualities, i. e. sufficient freedom from coke formationand soot depositing tendencies, a distillate fuel-should have a BQI of at least about `Thus a dis-` tillate fuel fraction of an M-C virgin gasoil having an API gravity of 34.6, a 10% distillation point of`490 F., a 50% point at 564 F'. and a point at 619 F. has a BQI of about 80. The cycle stock produced by cracking such gas oil and characterized by a gravity of 36.0 API, a 10% point of 368 F., a 50% point of 414 F. and a 90% point of 470 F. has a BQI of about 71. However, a distillate fuel produced by the cracking or coking of West Texas gas oilmay havev a BQI of only about 20, the BQI of some fractions being as low as 10. An object of the invention is to provide distillate fuels from high sulfur crudes Without interfering with maximum gasoline production, said distillate fuels havinga BQI of at least about 60.

Distillate` fuels usually boil in the range of about 350 to 750 F., the so-called heater, oils (for pot type and sleeve type burners) boiling chiefly in the range of 350 to about 550 F. or more (some having end points as high as up to about 700"` F.) and Diesel fuels boiling chiefly in the range ofabout 400 to 650 F., or more.` It is desirable to manufacture furnace oils of suiiiclently low sulfur content andhigh cetane number that they can also be utilized' as Diesel fuels. For

such use the cetane numberof the fuel should be `interfering with maximum `gasoline production, `said distillate fuels having a cetane numberofat least about 40 and preferably about 50 or timore.

An important object of the invention is to accomplish each of the above objects simultaneousf ly and at the` same time'to produce, in `addition to maximum yields" of-gasoline, ahmarketable 3 coke and a valuable by-product extract which may find important utilization in the agricultural and construction industries.

In practicing the invention a high sulfur crude oil or a charging stock consisting essentially of high sulfur crude oil, may be processed primarily for production of maximum ygasoline yields by the catalytic cracking of the gas oil fraction and the coking of the residual fraction under conditions which are now well known in the art. The gas oils produced in such operations are then extracted with HF at a temperature in the range of about 50 to 150 F. and'with an amount of HF in the range of about .O5 to 2 volumes, preferably about .5 volume, per Volume of gas oil charged. The extraction is preferably effected in a countercurrent system designed to provide intimate contact and adequate time of contact which may be in the range of about to 60 a minutes, e. g. about 3() minutes but which will Y depend somewhat upon the intimacy of contact.

Particularly in the case of coke still gas oil, which may constitute one of the largest refinery streams and which constitutes the most difficult problem., .thecontacting and/or Separation of HF and gas oil may be effected in the presence of a small amount of a light parafllnic hydrocarbon such as'normal hexane or a pentane or similar cut of light naphtha; Vsuch hydrocarbon is not primarily for the purpose of reducing viscosity but it has been found to minimize emulsion difficulties and to facilitate phase separation as Well as to facilitate solvent removal after the extraction step. Yields of gas oil raffinate obtainable in such extraction lprocesses. range from about 75% to 90% and the extract obtained has unique properties which may make it useful for impregnatin g compositions for the protection of wood and other fibrous materials against the action of termites, marine borers, etc.

The extraction effects a surprising improvement in the characteristics of the oil which are of such importance in the distillate fuel field without substantially changing the distillation temperature of the various boiling range fractions, particularly those fractions which are desiiedy in the distillate fuel field. The resulting fuel oil fractions are thus characterized by sul fur content not substantially exceeding about .5%. usually in the range of about .l to about 3%, a BQI of upwards of about 60 and a cetane number upwards of about 40 or 50. In addition vto these important improvements the fuel oil fractions are further improved by having a lower brominenumber, density, refractive index and specific dispersion. The improved BQI means that it has a remarkably lower tendency to deposit carbon on burning.

The invention will be more clearly understoody withdrawn through line I to catalytic cracking system l5 and a lighter-thangasoil fraction which is withdrawn through line l5 and subjected to known processes for the production of 4 high quality motor fuel. The virgin gas oil fraction may, if desired, be withdrawn with the residual fraction as a part of the reduced crude.

The coking of the reduced crude or residual fraction is essential for obtaining maximum gasoline and distillate fuel oils from the crude oil. No novelty is claimed in the coking operation per se since it is well known to those skilled in the art and it willnot be described in great detail.

Brieiiy, the process comprises the subjecting of the reduced crude to temperatures of the order of about 850 to about 1000 F., e. g. 900o F., at a pressure of about atmospheric to p. s. i., usually about 50 p. s. i., for suicient time of contact to convert the charge into solid coke, coke still gas oil and coke still naphtha with some formation of lighter hydrocarbons. The coke is removed at l1 and marketed as such. The coke still naphtha is removed at line i8 and may be catalytically reformed for effecting desulfurization and octane number improvement by conventional methods. The coke still gas oil, however, has presented the most difficult problem for petroleum refiners because it is not particularly ldesirable as a charging stock for thermal and catalytic cracking and because it possesses none of the essential characteristics required for meeting distillate fuel specifications.

The coke still gas oil is withdrawn through line "is and if it contains any moisture it should be dried by passage through drying towers or other conventional drying equipment. From line i9. the coke'still gas oil is introduced into HF extraction tower 2i] (which may be packed with l-inch carbon rings 2l supported on grid support 22) where it is intimately and countercurrently contacted with liquid HF introduced through line 23. The extraction may be effected in a batch or multiple batch system or in a continuous tower type reactor or in any other known It has been found however that best results are obtained when a small amount, for example about 2 to 20% or approximately 10%, of a light hydrocarbon or mixture of hydrocarbons of the butane to heptane boiling range, for example hexane, is'introduced either by line 2G below the coke still gas oil inlet or by line 25 with the gas oil charge, the former giving the bestresults.

The amount of solvent may be varied within the fairly wide range of about .05 volume to 2 volumes or more of HF per volume of coke still gas oil charged but from a quality yield standpoint it has been found that good results are obtained with from about .2 to about .5 volume of HF per volume of gas oil charged. Thus using approximately .3 volume of HF per volume of gasoil charged, a raffinate yield of about 81.5% has been obtained with a sulfur content of The extraction may be effected at ordinary atmospheric temperature or within the range of about 50 to 150 F; and the time of contact may be about l0 to fidminutes, e. g. about 30 ininutes, although shorter times may be employed if greater intimacy of contact is obtained.

The extract from the countercurrent extraction system is withdrawn through line 26 to extract stripper 2, which may be provided with suitable top'cooling or reflux means such for example as introduction of condensed at the upper part thereof. The extract stripper is provided vvith conventional heating means 2E which may besupplemented by the use of an inert stripping gas such as propane, butane, etc. The stripping gas and removed HF are withdrawn through line '29 and the extract material through line ammala 30. The nal extract maybe cntactedmwith ybauxite for decomposingany alkyl fluorides in accordance with conventional practice inthe HF alkylation art. This material has unique properties which may prove to be of importance in wood impregnating compounds and the manufacture of resins and plasticizers. Such extract may contain or 6% by weight of sulfur and it may be characterized by an A. P. I. gravityof about 6 to 8 with a boiling range higher than that of the charging stock. The extract itself may be subjected to a coking operation and when coked at about 1000 F. yields about 63% liquid product.'

13% coke, and 24% gas, the total liquid product containing about 6% and the coke about V3% of sulfur.

The rainate from the extraction system 20 is withdrawn through line 3| to raffinate stripper 32 which is provided with conventionalreboiler or heating means 33 and also with suitable top cooling or reilux means. A cooler and acid settler may be interposed in 3| for the separation and direct recycling of any HF that may be separated from the raffinate by such procedure and an inert stripping gas such as propane, butane or the like may supplement heat as a means for removing the HF from the railnate material. The HF and stripping gas leave stripper 32 through line 34 and may be combined with materials from line 29, the combined materials being cooled in cooler 35 and introduced, into settler 36. The separated HF may be withdraw from the settler through line 31, supplemented when necessary by makeup HF from line 38 for introduction through line 23 to extraction system 20. The upper hydrocarbon layer may be withdrawn from settler 36 through line 36 and at least a part of it may be withdrawn through line 40 or returned to low points in the stripping towers. At least a part of the hydrocarbons may be passed by lines 4l and 24 to a low point in the extraction tower 23 in place of or in addition to makeup hexane or light parainic hydrocarbon introduced through line 42.

The gas which may contain HzS, vented from the top of settler 36 through line 40a and/or the stream from line 40 may be processed in any known manner for recovering residual HF therefrom. For example, the gas stream from line 40a may be scrubbed with a lean oil under conditions for dissolving HF, the undissolved material may be vented from the top of the scrubber, the rich oil from the base of the scrubber may be heated to release the dissolved HF, the liberated HF may be returned to the system, and the denuded lean oil may be cooled and returned to the top of the scrubber (not shown). The stripped raffinate passes from the base of stripper 32 through line 43 to fuel oil fractionator 44 which is diagrammatically illustrated as a simple tower but which may consist of any conventional or known fractionation system provided with conventional reboiling and reflux means. Any remaining dissolved HF may be removed from the stripped rafinate bypassing it through line 45 to scrubber 46 into which a caustic solution is introduced by line 41 and turned by line 52 to the catalytic cracking unit I 5. The extraction step makes" these heavy ends particularly suitable as a charging stock for the catalytic cracking step. At least a part of the distillate fuel boiling range fraction may` also be introduced through lines 53 and -52 to cat-` alytic cracking unit I5.

`As 1a specific example, a West Texas crude was fractionated to give av 55% reduced crude characterized by an API gravity of 19.3, a sulfur content of 2.3% and a boiling range upwards of about 500 F. The reduced crude was Vsubjected to a coking which operation resulted in wet gas yield of 6.3 wt. percent, a coke' yield of 13.3%, a gasoline yield of about 10 volume percent and a coke still gas oil yield of about 75 volume percent, the latter having an API gravity of about 27.5, a wt. percent sulfur of about 1.8 and a boiling range of about 400 to about 750 F. Representative inspections on coke still .gas oil as charged to an HF extraction `unit andorra total raiiinate therefrom as charged to a fractionator are as follows:

Coke Still gas Dil Ra'inate Volume Per Cent on Original 100.0 81.5

API Gravity 27.1` 32.3

Weight Per Cent Suliur, 1.64 0. 5

BOI 46 77 Bromiue Number 24 5 Specific Dispersion l 129 Refractive Index 1.4983 1. 4814 Cetane Number 45 51 ASTM Distillation:

Initial Boiling Point 370 258 Maximum 750 1- Weight Per Cent Fluorne 0. 005

Per Cent S in heater oil boiling range Less than .05%

" act with the olei'lns of such charging stocks to um hydroxide or the like.

form alkyl fluorides; the extremely small amount of alkyl fluoride formation was surprising and although the raffinate may sometimes contain as much as .02% fluorine, a caustic wash is usually all that is required. Stripped extract may be contacted with bauxite for decomposing any residual alkyl fluorides and stripped raffinate may simply be scrubbed with aI solutionof sodi- Since most distillate fuelsare of narrower boiling range than the total raffinate it is` important to know the properties of the components of diierent boiling range in the total railinate. Inspections on seven fractions the solution .of morenon-sulfur compounds into of a representatlve raffinate are as follows: the extract phase.

4 Total out Raf- 1 2 3 4 5 Y 6 7 Bottoms nate Volume per cent on total `Raflinate 5.0 5.70 5. 1 5. 0 5. 2 5.- 2 Y 5. 2 61. 2 v weigmpercenrs 0.476 0.039 0. 039 0.058 0.034 0.122 0.172 0.217 0.690 0.4M. 32. 5 59. 2 42. 0 39. 5 37. 9 36. 4 35. 6 34. 7 23. 6 BQL 73. 5 100+ 90. 6 39. 0 35. 0 32. 4 31. 2 79.2 IBP 133 140 370 434 430 Y 432 496 514 493 160 404 456 481 504 524 536 '.1- 50 634 220 423 474 502 526 546 560 00 412 454 496 523 554 576 536 Max 726 436 520 543 530 532 503 614. ,ABQL 32 12.0 23.3 27.1 23.2 29.2 30.5v

The above information shows that the low boiling fractions are remarkably low in sulfur content containing only about .04%. The last line of the above tabulation shows the increase in BQI over that of the correspondingV fractions in the unextracted coke still gas oil.

The remarkable results accomplished by HF extraction of coke still gas oil are not obtained by processes heretofore known to the art. When distillate fuel fractions of coke still gas oil are treated with sulfuric acid, desulfurization is disappointingly low even at treats With as rnuch as pounds of 98% sulfuric acid per barrel (which is about ten times the amount of acid currently used for stabilizing furnace oils). The unique character of coke still gas oil is shown by the fact that HF extracts from virgin gas oils and even from cycle gas oils produced by thermal or catalytic cracking can be almost completely (99 U/'a or more) desulfurized by hydrogenation over cobalt molybdate catalyst at '750 F. and 300 p. s. i. g. pressure with a space velocity of about .5 and with 24,000 cubic feet per barrel of added hydrogen; only about 80% ofthe sulfur could thus be removed from HF extract from coke still gas oil. Apparently the coking process changes the nature of at least a part of the sulfur compounds in a high sulfur charge and creates a sulfur removal problem which is not encountered with virgin or cycle gas oils. It appears that the sulfur compounds in the 500 or 600 to 700" F. boiling range are most diilicult to remove by hydrogenation (hydrodesulfurization) and the invention is particularly applicable to such coke still gas oil fractions.

My HF extraction is surprisingly more effective on coke still gas oil than onV virgin gas oil, as shown by the following comparative data on ex- The sulfur and aromatics in coke still gas oil appear'to bemore soluble in HF than the corresponding compounds in Virgin gas oil of similar boiling point. There appears to be a loss offserlecm tivity when the amount of solvent is less than 10% or more than about 60 to 80% because of vom@ Per A- S- T- M- Per'Cent Cent API BQI Yield Sulfur v 10 50 90 Feed 0.45 -30. 3 574 656 748 73 94. 3 0. 24 31. 2 584 658 742 72 Extract 5. 7 2. 1 1.7

Extractionof coke still gas oil chiefly of West Texas origin with 33 volume percent HF gave the following results:

Volume Per A" s T' M' BQI Percnt Cent "API I meld Sulfur l0 50 90 0.0 l. 64 27. l 490 025 746 48 "81.'5 0.48 32.6 482 631 748 84 Extract 18. 5 5. 80 (i. l

The raffinate of the M-C gas oil showed an actual decrease in BQI by the extraction step while in the case of high sulfur coke still gas oil the BQI was increased from 48 to l84, the coke still rafnateBQl being materially higher than that of virgin M-C oils.

Now with regard to the significance of the BQI, it is well known thatv the various renery stocks in the distillate fuel boiling range are by no means of the same quality. Some highly refined stocks give troublenfree performance in the most critical type burners while others are wholly unsatisfactory giving large deposits in relatively short periods of time. The need for a test method to rate the performance of a furnace oil in a burner is not unlike the earlier need of the industry fora device to measure the performance of gasolines in internal combustion engines. In this latter case the conventional octane scale has proven of great utility'. With this thought in mind successful eiforts were made to set up a somewhat`si1nilar scale for rating the performanc'efofA distillate fuels in burners. The "test burner iselected wasv iav Coleman Model 821B Space' HeaterQThis burner was chosen because it is typical of the most sensitive class of burners used commercially; The standard burner test involves determining the weight of the total burner deposits when l gallons of fuel are burned at the rate of 0.3 gallon per hour employing 0.06 inch of Water draft. The theoretically perfect fuel would, of course, give no burner deposits; such a fuel is arbitrarily defined as having a BQI of 100. The most highly refined selected refinery stocks, however, merely approach this ideal giving burner deposits of approximately 8 grams; such distillate fuels on this scale have a BQI of 100 minus 8 or 92. One of the poorer refinery stocks gives deposits as high as 90 grams; such a fuel has a BQI of 100 minus 90 or only 10. Thus, BQI is a measure of distillate fuel performance and may be dened as 100 minus the number of grams of burner deposits accumulated when 10 gallons of fuel are burned in the test burner at the rate and under the conditions mentioned above. The development of a process or method which converts stocks which are now unsatisfac- Y `be as follows:

Vol. Per Per A' S T M' C t cent of cent APL BQI Neo- Rai. Sulfur 10 50 90 Heater O11- 15 0; 06 39. 9 89 439 471 515 53 Furnace..-" 2B 0. 16 39. 0 86 424 495 598 54 In addition to the above it should be noted that the distillate fuels produced by this invention have such good odor and such low copper numbers (about 2 or 3) that additional sweetening may be entirely unnecessary.

The data hereinabove set forth illustrate the remarkable and unpredictable results obtainable by HF extraction of coke still gas oil from high sulfur crudes. If the virgin gas oil fromthe high sulfur crude is charged to a catalytic cracking unit instead of a coking unit, the cycleoil produced in the catalytic cracking operation may be extracted with HF to give results which are advantageous but which are by no meansthe equivalent of the extraction of coke still gas oil.

For example, a cycle gas oil from the catalytic cracking of a charge containing a large portion of West Texas origin was extractedwith 47 volume percent HF with following results:

V l P C l A. S. T. M.

o. er Per ent 1 Cent "Sulfur PI BQI y vFeed l. 35 25. 7 -10 476 534 667 Rainate. 79. 1 l 0. 33 32. 7 59. 4 464 525 640 Extract `20.5 4.67 1.5 496 639 It will be noted that the BQI of the raffinate was improved to a remarkable extent but not to the quality obtainable by extracting coke still oil. When the cycle oil was dividedinto a light catalytic cycle oil fraction and a heavy catalytic cycle oil fraction, these two "fractions were separately extracted with HF using about 50% HF by volume i 10 on the light fraction and about 40% HF by volume on the heavier fraction and the following results were obtained:

The light fraction did not result inas high a BQI as obtained with coke still gas oil and the heavier fractionshows much less desulfurizration than obtainable with coke still gasoil.

`The coke still gas oil itself may be catalytically cracked and the cycleoil thus producedmaywbe extracted with HF. When coke still gas oil was thus catalytically cracked under` conventional conditions the conversion was 42% and the properties of the cycle oil before and after HF extraction were found to be asfollows:

V1 P C t A snnM. o er en Per Cent Sulfur API BQI i Feed 1. 04 24. 8 10 489 562 692 Ranate- 1 76. 6 0. 43 31. 6 60 474 552 675 Extract 22. 6 4. 46 0 When the coke still gas oilwas first extracted withHF .and only the rainate subjected tc catalytic cracking the conversion was considerably higher, 55%, and the properties 0f the cycle gas oil before and after extraction were as follows:

V 1 P C t A. S. T. M.

o er en Per Cent ulur API BQI lfeedi.; 0.71 28. 9 28 486 540 660 Rainone.-." 87.1 0.31 32. 7 62 481 535 639 Extract 12. 3 3. 1 0

The catalytic cracking may be effected in xed bed, moving bed or powdered catalyst systems all of which are well known to the art and which require no detailed description. The socalled fluid catalytic cracking process is preferred, such for example, as that illustrated 0n page 63 of the Petroleum Engineer, January, 1945, and

described by Murphree et al. inOil and Gas J'ournal of March3, 1945, at page 64 et seq.. The catalyst may be an acid treated montmorillonite clay or of the synthetic silicaalumina `or silica' magnesia type havinga small particle size. The catalyst to oil ratios may be in the rangeof 2:1 to 20:1 on a weight basis, the crackingternperature may be in the range of about 800 to 1000o F.; e. g. about 900 F. at a gauge pressure of the order 11 of to 15 pounds per square inch and with a weight space velocity in the range of .2 to poundsof oil charged per hour per pound of catalyst in the reactor.l The charging stock passes upwardly through the reactor at a velocity in the range of about 1 to 3 feet per second and sufficiently low to maintain the catalyst in dense phase turbulent suspension, a portion of the catalyst being continuously withdrawn to a separate regenerator from which regenerated catalyst is constantly returned to the reactor. Since no invention is claimed in the catalytic cracking step per se, no further description of it is necessary.

Gasoline is withdrawn from the catalytic cracking system through line 54 and lighterthan-gasoline products through line 55. The heaVier-than-gasoline components, usually referred to as catalytic cycle oil, are withdrawn through line 55 and at least a portion thereof 'may be withdrawn from the system through line Yagain the optimum HF to oil ratio for the extraction step appears to be in the general vicinity of .5 volume of HF per volume of oil undergoing extraction. Under such conditions the raiiinate yield is about 80 to 85% and representative inspections ofthe total cycle gas oil, raffinate and extract respectively are as hereinabove tabulated. As hereinabove pointed out, at least a portion of the I-IF extracted coke still gas oil may be charged to the catalytic cracking step. It has been found that when unextracted coke still gas oil (from West Texas crude) is charged to the catalytic cracking step employing an activated clay or natural cracking catalyst,.the activity of the catalyst decreases quite rapidly, the amount of conversion correspondingly decreases and the weight percent of coke based on charge rapidly increases. However, when such coke still gas oil is extracted with HF to give about 81.5% raiiinate as hereinabove described and the extracted gas Aoil is charged to catalytic cracking, the initial conversion is considerably greater. The effect of the extraction step on catalyst deterioration in the cracking step is shown by the following tabulated results of an experimental program:

` Catalyst activity .as herein employed means the number of parts by Weight of a fresh reference catalyst that'would be required to obtain the same extent of conversion as is effected by 100 parts by weight of the catalyst being rated under the same operating conditions. (De terniinahon of Activity and selectivity of Cracking Catalyst presented by'Shankland and Schmitkons at November 10,1947, meeting of American Petroleum Institute.) The decline of catalyst activity with coke still gas oil enormously decreases the conversion which can be elected The product distribution in the catalytic crackmg step is likewise remarkably improved by the HF extraction step as shown by the following results:

Although the light cycle oil from the catalytic cracking of FF extracted gas oil is of somewhat lower quality for distillate fuel oil preparation than extracted coke still gas oil itself, certain fractions thereof will meet BQI and sulfur specications and the BQI impro-vement in particular is remarkable. It should be noted that the HF extraction lowers the coke yield to less than half of its original value, markedly increases the gasoline yield and produces a gasoline which, with the addition of tetraethyl lead in amounts of 1 cc. and 3 cc. respectively, is even superior to the gasoline produced from unextracted coke still gas oil.

It should be emphasized that the HF extraction in all cases is effected without the necessity of employing BFa or other additives which so greatly increase the cost and difliculty of refining.

While preferred examples of the invention have been described in considerable detail it should be understood that the invention is not limited thereto since numerous alternative procedures and operating conditions will be apparent from the above description to those skilled in the art.

I claim:

1. A method of obtaining a high quality distillate fuel, which method comprises coking a virgin high boiling fraction of a high sulfur crude oil, effecting said coking at a. temperature between about 850 F. and about 1000 F. at a pressure between about 15 and about 100 p. s. i. to produce principally a coke still gas oil having an A. P. I. gravity below 30, more than 1 weight percent of sulfur and a, burning quality index less than 50, extracting said coke still gas oil with liquid hydrogen fluoride in an amount between about 20 and about 50 percent by volume, based on said coke still gas oil, at a temperature between about 50 F. and about 150 F. to produce a raflinate, fractionally distilling said raiiinate to obtain a distillate fuel oil fraction boiling between about 350 F. and about 650F., the last-named fraction having a sulfur content not in excess of about 0.3 weight percent and a burning quality index of at least 75.

2. The method of producing high quality distillate fuel from a coke still gas oil obtained by the coking of a high boiling fraction of a high sulfur crude oil at a temperature in the range of about 850 F. t0 about 1000 F. at a pressure between about 15 and about 100 pounds per square inch to produce principally a coke still gas oil having more than one weight per cent oi sulfur and a burning quality index not higher than about 50, which method comprises contacting said coke still gas oil with liquid hydrogen uoride at a temperature in the range of about 50 F. to 150 F. with a hydrogen fluo-ride to oil volume ratio which is greater than .1:1 and less than .6:1 with a time of contact less than 60 minutes but Sunicient to produce a raffinate having a sulfur content not substantially in excess of about 0.5 weight per cent, separately removing hydrogen fluoride from the raffinate and extract produced in the contacting step, and fractionating the hydrogen iiuoride-iree raffinate to obtain a distillate fuel oil fraction boiling chiefly in the range of 350 F. to 650 F., said distillate fuel oil fraction having a sulfur content not in excess of about 0.3 weight per cent and a burning quality index of at least about 75. Y

3. The method of producing high quality distillate fuel from a coke still gas oil :produced by coking a high boiling fraction of a high sulfur crude oil at a temperature in the range of about 850o F. to about 1000 F. and a pressure in the range of about 15 to 100 -pounds per square inch to produce principally a coke still gas oil containing more than one weight per cent of sulfur and having a burning quality index not higher than about 50, which method comprises extracting said coke still gas oil with liquid hydrogen uoride in an amount between about and about 50 per cent by volume, based on said coke still gas oil, at a temperature between about 50 F. and 150 F., employing in the extraction step a contact time which is less than 60 minutes and sufficient with the intimacy of contact employed to produce a yield in the range of 75% to 90% of a rafnate which when freed from ,hydrogen fluoride is characterized by a sulfur content not higher than about .5 weight per cent and a burning quality index of at least about 60, and separately removing hydrogen fluoride from the raffinate and extract produced in the extraction step.

4. The method of producing, from a high sul- Y F. under a pressure in the range of about atmospheric to 100 pounds per square inch for a time of contact suflicient to effect production of coke still gas oil, components lower boiling than gas oil and coke, said coke still gas oil having a sul- 14 fur content higher than one weight per cent and a burning quality index not substantially higher than about 50, extracting said coke still gas oil with liquid hydrogen fluoride at a temperature in the range of about F. to 150 F., at a pressure suiicient to maintain liquid phase extraction conditions with an amount of liquid Y hydrogen iluoride between about 20 and about 50 per cent by volume based on said coke still gas oil and with a contact time in the extraction step of less than minutes but suiicient with the intimacy of Contact employed to [produce a yield in the range of to 90% of airainate having a sulfur content not substantially in excess of about 0.5 weight per cent and a burning quality index of at least about 60, and separately removing hydrogen iluoride from extract and rainate produced in the extraction step.

5. The method of claim 4 which includes the further step of diluting the coke still gas oil in the extraction step with about 2 to 20 per cent` of a light hydrocarbon of the butane to heptane boiling range.

v6. The method of claim 4 which includes the further step of coking the extract after removal of hydrogen fluoride therefrom.

7. The method of claim 4 which includes the further step of catalytically cracking the raffinate after removal of hydrogen fluoride therefrom by contacting said raffinate with a solid cracking catalyst of the class consisting of acid treated clay, synthetic silica alumina and silica magnesia ata temperature in the range of about 800 F. to about 1000 F.

NATHAN FRAGEN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PA'IENTS Number Name Date 2,064,842 Lowry et al Dec. 22, 1936 2,352,236 Thomas June 27, 1944 2,375,675 Matuszak May 8, 1945 2,378,762 Frey June 19, 1945 2,434,623 Meadow et al Jan. 13, 1948 2,479,238 I-Iolm et a1. Aug. 16, 1949 

1. A METHOD OF OBTAINING A HIGH QUALITY DISTILLATE FUEL, WHICH METHOD COMPRISES COKING A VIRGIN HIGH BOILING FRACTION OF A HIGH SULFUR CRUDE OIL, EFFECTING SAID COKING AT A TEMPERATURE BETWEEN ABOUT 850*F. AND ABOUT 1000*F. AT A PRESSURE BETWEEN ABOUT 15 AND ABOUT 100 P.S.I. TO PRODUCE PRINCIPALLY A COKE STILL GAS OIL HAVING AN A. P. I. GRAVITY BELOW 30, MORE THAN 1 WEIGHT PERCENT OF SULFUR AND A BURNING QUALITY INDEX LESS THAN 50, EXTRACTING SAID COKE STILL GAS OIL WITH LIQUID HYDROGEN FLUORIDE IN AN AMOUNT BETWEEN ABOUT 20 AND ABOUT 50 PERCENT BY VOLUME, BASED ON SAID COKE STILL GAS OIL, AT A TEMPERATURE BETWEEN ABOUT 50*F. AND ABOUT 150*F. TO PRODUCE A RAFFINATE, FRACTIONALLY DISTILLING SAID RAFFINATE TO OBTAIN A DISTILLATE FUEL OIL FRACTION BOILING BETWEEN ABOUT 350*F. AND ABOUT 650*F., THE LAST-NAMED FRACTION HAVING A SULFUR CONTENT NOT IN EXCESS OF ABOUT 0.3 WEIGHT PERCENT AND A BURNING QUALITY INDEX OF AT LEAST
 75. 